ch 18 - prokaryotic gene regulation

Question 1

what contributes to the genetic diversity of bacteria (prokaryotes)

Answer 1

rapid reproduction, mutation, and genetic recombination

Question 2

bacterial chromosome

Answer 2

a circular DNA molecule with few associated proteins

Question 3

plasmids

Answer 3

smaller circular DNA molecules that can replicate independently of the bacterial chromosome
contains small number of genes not required for survival
contains genes that give bacteria an advantage
replicate separately from other dna

Question 4

how do bacterial cells divide

Answer 4

by binary fission
preceded by replication of the bacterial chromosome

Question 5

recombination in bacteria

Answer 5

three processes bring bacterial DNA from different individuals together
conjugation
transduction
transformation
bacteria try to pass on genome

Question 6

recombination - conjugation

Answer 6

bacteria and bacteria

Question 7

8recombination - transduction

Answer 7

bacteria and virus

Question 8

recombination - transformation

Answer 8

bacteria and nothing
naked dna

Question 9

bacteria response to environment

Answer 9

bacteria can cope with environmental fluctuations by exerting metabolic control
cells can turn on or off soecific genes or adjust the activity of enzymes already present

Question 10

operons

Answer 10

basic mechanism for gene expression
genes often clustered into operons
operons can be turned on or off by different proteins that interact directly with the DNA near the region of the gene

Question 11

operon parts

Answer 11

regulatory/repressor gene codes for the repressor protein
promotor site - attachment site for RNA polymerase
operator site - attachment site for repressor protein
structural genes - codes for the proteins of interest

Question 12

repressible operons

Answer 12

the gene that is coded for is usually on
binding of a specific repressor protein to the operator shuts off transcription
repress expression with attachment

Question 13

inducible operon

Answer 13

usually off
binding of an inducer to an active repressor protein inactivates the repressor and turns ON transcription

Question 14

repressible operon - trp operon

Answer 14

trp operon normally on
RNA polymerase can bind to promoter and transcribe the genes of that operon
trp operon usually on and codes for proteins that synthesize tryptophan
repressed by pressence of tryptophan

Question 15

how does tryptophan repress trp

Answer 15

regulatory gene mRNA makes trp repressor protein but protein is inactive
typically RNA polymerase moves along operator and genes of operon
when tryptophan is present it can bind to protein at nonactive site
protein is activated and binds to operator on DNA
RNA polymerase can therefore no longer move passed promoter
more tryptophan = more operators turned off = less tryptophan made

Question 16

lac operon

Answer 16

lactose available/present to E.coli if host drinks milk
lactose broken down to monosaccharides by enzyme beta - galactosidase
beta - galactosidase not always made by E. coli
only made when necessary

Question 17

lactose absent

Answer 17

repressor is active and operon is odd
the lac repressor is innately active and RNA polymerase is off bc no need to make enzymes to digest lactose since no lactose is present

Question 18

lastose present

Answer 18

when lactose is present it binds to regulatory protein which inactivates it
then the RNA polymerase can move passed promoter and enzymes that break down lactose are formed

Question 19

importance of lac operon

Answer 19

many bacterial genes are under negative control by repressor proteins
introduced a fundamentally important idea : gene expression is reguated by physical contact between regulatory proteins and specific regulatory sites in DNA

Question 20

when we need to transcribe beta-galactosidase, two molecules are necessarary

Answer 20

cyclic AMP (CAMP)
binds to CAP+
and RNA polymerase
CAMP + CAP complex binds near polymerase and helps get polymerase in the right place

Question 21

lactose and glucose levels relationship

Answer 21

lactose is only used as an energy source when a better carbohydrate source isn’t present
when glucose is present, CAMP levels are low, so they can’t bind to CAP and initiate enzyme production = no transcription